The present invention relates to the unloading of bulk bags used as containers for dry or moist particulate materials. The present invention more particularly relates to the unloading of bulk bag containers fabricated from cloth like material, such as woven polyester material, which is usually sewn in a cubical configuration.
Bulk bags made of heavy cloth material have been known in the art for sometime. It has also been known to provide the bag with heavy corner straps which support the bag when it is hung in a tower like support frame. The opposite end of the bag typically has a central outlet spout which is aligned with a discharge unit, for example a conveyer, hopper or the like, into which the material in the bag is intended to be discharged. Prior to discharge, the spout is maintained in a closed position, typically by tying-off of the spout.
To discharge the bag, the bag is hung in the support frame and the spout engaged with the discharge unit. The spout is opened and the particulate material flows via gravity through the spout. It is often desirable to control flow of material from the spout, for example, to permit batch weighing or to permit re-tying of the bag. Various types of bag closing devices, examples of which are illustrated in FIGS. 1–3, have been employed. In the device of FIG. 1, opposed bars, either flat or cylindrical, are moved together by fluid cylinders. As the spout is closed, it flattens in the direction of the arrows in FIG. 1. As a result, the flattened, wide spout is difficult to re-tie, particularly if the spout is short. The device of FIG. 2 attempts to overcome such by providing substantially v-shaped opposed bars, as described in U.S. Pat. No. 5,787,689. However, at the two points of overlap between the opposed bars, the bag is susceptible to pinching which may cut the bag or the bag may roll out between the overlapped bars. Referring to FIG. 3, a “claw” like device is shown. The bag is again susceptible to pinching in such a device. Additionally, in some applications, for example where the particulate material is dense, a significant amount of torque is required to closed the opposed claw members.
Accordingly, there is a need for an apparatus which assists in restricting a bag spout while reducing the likelihood of pinching of the spout.
It would also be desirable to provide a mechanical pinch valve for various other applications.